This invention relates to thyristors and, more particularly to gold doped fast turnoff thyristors.
Since their introduction, thyristors have become more popular as circuit designers have continued to employ them in new and different ways. As new applications for thyristors are developed, greater emphasis is placed on improving the performance of the devices under demanding conditions of operation. Different applications require that the emphasis be placed on different characteristics of the device. For example, some potential applications will become commerically feasible only if the cost of the thyristors can be reduced. Other applications require that the devices be able to withstand higher reverse voltages or that they switch from a conductive to a nonconductive state more rapidly. Thus, the device designer is faced with a multifaceted problem.
One of the principal concerns of the device designer is the interrelationship among the various device characteristics. For example, it is known that if gold is diffused into the interior of a thyristor, the minority carrier lifetime is decreased and thus turnoff time is reduced. However, the effect of the gold diffusion step on the cost of the device must be considered. Further, heavy blanket gold doping increases thyristor leakage current. Yet, in an effort to simplify and reduce the number of manufacturing steps, gold diffused thyristors have generally been manufactured with a blanket gold diffusion process. Consequently, excessive leakage current is sometimes a problem in gold diffused thyristors. Processes for localized gold diffusion have been developed. See, for example, U.S. Patent Application Ser. No. 405,489, filed on Oct. 11, 1973, in the name of Richard W. Kennedy, et al, and assigned to the assignee of the present invention, now U.S. Pat. No. 3,941,625. However, these processes frequently necessitated the addition of several manufacturing steps so that, while thyristors with good electrical characteristics were provided, cost sometimes became a problem.
It is, therefore, an object of this invention to provide a thyristor that possesses the rapid turnoff capability characteristic of gold doped devices yet is less expensive and exhibits a smaller leakage current than heretofore known gold doped devices. It is also an object of this invention to provide a method for making the subject thyristor.